Desulfurization and aromatic saturation of feedstreams containing refractory organosulfur heterocycles and aromatics

ABSTRACT

A process for the hydrodesulfurization (HDS) of multiple condensed ring heterocyclic organosulfur compounds present in petroleum and petrochemical streams and the saturation of aromatics over noble metal-containing catalysts under relatively mild conditions. The noble metal is selected from Pt, Pd, Ir, Rh and polymetallics thereof. The catalyst system also contains a hydrogen sulfide sorbent material.

This application claims the benefit of U.S. provisional application Ser.No. 60/024,737, filed Aug. 23, 1996.

FIELD OF THE INVENTION

The present invention relates to a process for the hydrodesulfurization(HDS) of multiple condensed ring heterocyclic organosulfur compoundspresent in petroleum and petrochemical streams and the saturation ofaromatics over noble metal-containing catalysts under relatively mildconditions. The noble metal is selected from Pt, Pd, Ir, Rh andpolymetallics thereof. The catalyst system also contains a hydrogensulfide sorbent material.

BACKGROUND OF THE INVENTION

Hydrodesulfurization is one of the fundamental processes of the refiningand petrochemical industries. The removal of feed sulfur by conversionto hydrogen sulfide is typically achieved by reaction with hydrogen overnon-noble metal sulfides, especially those of Co/Mo and Ni/Mo, at fairlysevere temperatures and pressures to meet product qualityspecifications, or to supply a desulfurized stream to a subsequentsulfur sensitive process. The latter is a particularly importantobjective because some processes are carried out over catalysts whichare extremely sensitive to poisoning by sulfur. This sulfur sensitivityis sometimes sufficiently acute as to require a substantially sulfurfree feed. In other cases environmental considerations and mandatesdrive product quality specifications to very low sulfur levels.

There is a well established hierarchy in the ease of sulfur removal fromthe various organosulfur compounds common to refinery and petrochemicalstreams. Simple aliphatic, naphthenic, and aromatic mercaptans,sulfides, di- and polysulfides and the like surrender their sulfur morereadily than the class of heterocyclic sulfur compounds comprised ofthiophene and its higher homologs and analogs. Within the genericthiophenic class, desulfurization reactivity decreases with increasingmolecular structure and complexity. While simple thiophenes representthe more labile sulfur types, the other extreme, sometimes referred toas "hard sulfur" or "refractory sulfur," is represented by thederivatives of dibenzothiophene, especially those mono- anddi-substituted and condensed ring dibenzothiophenes bearing substituentson the carbons beta to the sulfur atom. These highly refractory sulfurheterocycles resist desulfurization as a consequence of stericinhibition precluding the requisite catalyst-substrate interaction. Forthis reason these materials survive traditional desulfurization andpoison subsequent processes whose operability is dependent upon a sulfursensitive catalyst. Destruction of these "hard sulfur" types can beaccomplished under relatively severe process conditions, but this mayprove to be economically undesirable owing to the onset of harmful sidereactions leading to feed and/or product degradation. Also, the level ofinvestment and operating costs required to drive the severe processconditions may be too great for the required sulfur specification.

A recent review (M. J. Girgis and B. C. Gates, Ind. Eng. Chem., 1991,30, 2021) addresses the fate of various thiophenic types at reactionconditions employed industrially, e.g., 340-425° C. (644-799° F.),825-2550 psig. For dibenzothiophenes the substitution of a methyl groupinto the 4- position or into the 4- and 6-positions decreases thedesulfurization activity by an order of magnitude. These authors state,"These methyl-substituted dibenzothiophenes are now recognized as theorganosulfur compounds that are most slowly converted in the HDS ofheavy fossil fuels. One of the challenges for future technology is tofind catalysts and processes to desulfurize them."

M. Houalla et al, J Catal., 61, 523 (1980) disclose activity debits of1-10 orders of magnitude for similarly substituted dibenzothiophenesunder similar hydrodesulfurization conditions. While the literatureaddresses methyl substituted dibenzothiophenes, it is apparent thatsubstitution with alkyl substituents greater than methyl, e.g.,4,6-diethyldibenzothiophene, would intensify the refractory nature ofthese sulfur compounds. Condensed ring aromatic substituentsincorporating the 3,4 and/or 6,7 carbons would exert a comparablenegative influence. Similar results are described by Lamure-Meille etal, Applied Catalysis A: General, 131, 143, (1995) based on analogoussubstrates.

Mochida et al, Catalysis Today, 29, 185 (1996) address the deepdesulfurization of diesel fuels from the perspective of process andcatalyst designs aimed at the conversion of the refractory sulfur types,which "are hardly desulfurized in the conventional HDS process." Theseauthors optimize their process to a product sulfur level of 0.016 wt. %,which reflects the inability of an idealized system to drive theconversion of the most resistant sulfur molecules to extinction.Vasudevan et al, Catalysis Reviews, 38, 161(1996) in a discussion ofdeep HDS catalysis report that while Pt and Ir catalysts were initiallyhighly active on refractory sulfur species, both catalysts deactivatedwith time on oil.

Environmental and regulatory initiatives are also requiring lower levelsof total aromatics in hydrocarbons and, more specifically, the multiringaromatics found in distillate fuels and heavier hydrocarbon products(i.e., lubes). The maximum allowable aromatics level for U.S. on-roaddiesel, CARB reference diesel and Swedish Class I diesel are 35, 10 and5 vol. %, respectively. Further, the CARB and Swedish Class I dieselfuels allow no more than 1.4 and 0.02 vol. % polyaromatics,respectively.

Two types of process schemes are commonly employed to achievesubstantial HDS/ASAT of distillate fuels and both are operated atrelatively high pressures. One is a single stage process using Ni/Mo orNi/W sulfide catalysts operating at pressures in excess of 800 psig. Toachieve high levels of saturation pressures in excess of 2,000 psig arerequired. The other is a two stage process in which the feed is firstprocessed over Co/Mo, Ni/Mo or Ni/W sulfide catalyst at moderatepressure to reduce heteroatom levels while little aromatics saturationis observed. After the first stage the product is stripped to remove H₂S, NH₃ and light hydrocarbons. The first stage product is then reactedover a Group VIII metal hydrogenation catalyst at elevated pressure toachieve aromatics saturation. The two stage processes are typicallyoperated between 575 and 1,000 psig.

In light of the above, there is a need for improveddesulfurization/aromatic saturation process for treating feedstreams sothat they can meet the ever stricter environmental regulations.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a process forthe substantially complete desulfurization of a stream selected frompetroleum and chemical streams containing condensed ring sulfurheterocyclic compounds and the saturation of aromatic compounds of saidstream, which process comprises contacting said stream, at temperaturesfrom about 40° C. to 500° C. and pressures from about 100 to 3,000 psig,with a catalyst system comprised of: (a) a catalyst comprised of a noblemetal selected from the group consisting of Pt, Pd, Ir, Rh, andpolymetallics thereof, on an inorganic refractory support; and (b) ahydrogen sulfide sorbent material.

In a preferred embodiment of the present invention, the noble metal isselected from Ir, Pt, Pd, and polymetallics thereof.

In another preferred embodiment of the present invention thehydrodesulfurization catalyst and the hydrogen sulfide sorbent arepresent in a single mixed bed.

In yet another preferred embodiment of the present invention thehydrogen sulfide sorbent material is selected from supported andunsupported metal oxides, spinels, zeolitic materials, and layereddouble hydroxides.

DETAILED DESCRIPTION OF THE INVENTION

Feedstocks suitable for being treated by the present invention are thosepetroleum based feedstocks which contain condensed ring sulfurheterocyclic compounds, as well as other ring compounds, includingmulti-ring aromatic and naphthenic compounds. Such compounds aretypically found in petroleum streams boiling in the distillate range andabove. Non-limiting examples of such feeds include diesel fuels, jetfuels, heating oils, and lubes. Such feeds typically have a boilingrange from about 150 to about 600° C., preferably from about 175 toabout 400° C. It is preferred that the streams first be hydrotreated toreduce sulfur contents, preferably to less than about 1,000 wppm, morepreferably less than about 500 wppm, most preferably to less than about200 wppm, particularly less than about 100 wppm sulfur, ideally to lessthan about 50 wppm. It is highly desirable for the refiner to upgradethese types of feedstocks by removing as much of the sulfur as possible,as well as to saturate aromatic compounds.

It is well known that so-called "easy" sulfur compounds, such asnon-thiophenic sulfur compounds, thiophenes, benzothiophenes, andnon-beta dibenzothiophenes can be removed without using severe processconditions. The prior art teaches that substantially more severeconditions are needed to remove the so-called "hard" sulfur compounds,such as condensed ring sulfur heterocyclic compounds which are typicallypresent as 3-ring sulfur compounds, such as beta and di-betadibenzothiophenes. An example of a typical three ring "hard" sulfurcompound found in petroleum streams is 4,6-diethyldibenzothiophene.While the desulfurization process of the present invention is applicableto all sulfur bearing compounds common to petroleum and chemicalstreams, it is particularly suitable for the desulfurization of theleast reactive, most highly refractory sulfur species, particularly theclass derived from dibenzothiophenes, and most especially the alkyl,aryl, and condensed ring derivatives of this heterocyclic group,particularly those bearing one or more substituents in the 3-, 4-, 6-,and 7-positions relative to the thiophenic sulfur. The process of thepresent invention will result in a product stream with substantially nosulfur. For purposes of this invention, the term, "substantially nosulfur", depends upon the overall process being considered, but can bedefined as a value less than about 1 wppm, preferably less than about0.5 wppm, more preferably less than about 0.1 wppm, and most preferablyless than about 0.01 wppm as measured by existing, conventionalanalytical technology.

Catalysts suitable for use in the present invention are those comprisedof a noble metal selected from the group consisting of Pt, Pd, Ir, Rh,and polymetallic compounds thereof on an inorganic refractory support.Preferred noble metals are Ir, Pt and Pd, and polymetallics thereof. Thenoble metal will be highly dispersed and substantially uniformlydistributed on a refractory inorganic support. Various promoter metalsmay also be incorporated for purposes of selectivity, activity, andstability improvement. Non-limiting examples of such promoters that maybe used herein include those selected from the group consisting of Re,Cu, Ag, Au, Sn, Zn, and the like.

Suitable support materials for the catalysts and hydrogen sulfidesorbents of the present invention include inorganic, refractorymaterials such as alumina, silica, silicon carbide, amorphous andcrystalline silica-aluminas, silica-magnesias, aluminophosphates, boria,titania, zirconia, and mixtures and cogels thereof. Preferred supportsinclude alumina and the crystalline silica-aluminas, particularly thosematerials classified as clays or zeolitic materials, and more preferablycontrolled acidity zeolitic materials, including aluminophosphates,modified by their manner of synthesis, by the incorporation of aciditymoderators, and post-synthesis modifications such as demetallation andsilylation. For purposes of this invention particularly desirablezeolitic materials are those crystalline materials having micropores andinclude conventional zeolitic materials and molecular sieves, includingaluminophosphates and suitable derivatives thereof. Such materials alsoinclude pillared clays and layered double hydroxides.

The metals may be loaded onto these supports by conventional techniquesknown in the art. Such techniques include impregnation by incipientwetness, by adsorption from excess impregnating medium, and by ionexchange. The metal bearing catalysts of the present invention aretypically dried, calcined, and reduced; the latter may either beconducted ex situ or in situ as preferred. The catalysts need not bepresulfided because the presence of sulfur is not essential tohydrodesulfurization activity and activity maintenance. However, thesulfided form of the catalyst may be employed without harm and in somecases may be preferred if the absence of catalyst sulfur contributes tothe loss of selectivity or to decreased stability. If sulfiding isdesired, it can be accomplished by exposure to dilute hydrogen sulfidein hydrogen until sulfur breakthrough is detected.

Total metal loading for catalysts of the present invention is in therange of about 0.01 to 5 wt. %, preferably about 0.1 to 2 wt. %, andmore preferably about 0.15 to 1.5 wt. %. For bimetallic noble metalcatalysts similar ranges are applicable to each component; however, thebimetallics may be either balanced or unbalanced where the loadings ofthe individual metals may either be equivalent, or the loading of onemetal may be greater or less than that of its partner. The loading ofstability and selectivity modifiers ranges from about 0.01 to 2 wt. %,preferably about 0.02 to 1.5 wt. %, and more preferably about 0.03 to1.0 wt. %. Chloride levels range from about 0.3 to 2.0 wt. %, preferablyabout 0.5 to 1.5 wt. %, and more preferably about 0.6 to 1.2 wt. %.Sulfur loadings of the noble metal catalysts approximate those producedby breakthrough sulfiding of the catalyst and range from about 0.01 to1.2 wt. %, preferably about 0.02 to 1.0 wt. %.

The hydrogen sulfide sorbent of this invention may be selected fromseveral classes of material known to be reactive toward hydrogen sulfideand capable of binding same in either a reversible or irreversiblemanner. Metal oxides are useful in this capacity and may be employed asthe bulk oxides or may be supported on an appropriate support.Representative metal oxides include those of the metals from Groups IA,IIA, IB, IIB, IIIA, IVA, VB, VIB, VIIB, VIII of the Periodic Table ofthe Elements. The Periodic Table of the Elements referred to herein isthat published by Sargent-Welch Scientific Company, Catalog No. S-18806,Copyright 1980. Representative elements include Zn, Fe, Ni, Cu, Mo, Co,Mg, Mn, W, K, Na, Ca, Ba, La, V, Ta, Nb, Re, Zr, Cr, Ag, Sn, and thelike. The metal oxides may be employed individually or in combination.The preferred metal oxides are those of Ba, K, Ca, Zn, Co, Ni, and Cu.Representative supported metal oxides include ZnO on alumina, CuO onsilica, ZnO/CuO on kieselguhr, and the like. Compounds of the Group IAand IIA metals capable of functioning as hydrogen sulfide sorbentsinclude, in addition to the oxides, the hydroxides, alkoxides, andsulfides. These systems are disclosed in the following patents of Bairdet al., incorporated herein by reference: U.S. Pat. No. 4,003,823; U.S.Pat. No. 4,007,109; U.S. Pat. No. 4,087,348; U.S. Pat. No. 4,087,349;U.S. Pat. No. 4,119,528; U.S. Pat. No. 4,127,470.

Spinels represent another class of hydrogen sulfide sorbents useful inthis invention. These materials are readily synthesized from theappropriate metal salt, frequently a sulfate, and sodium aluminate underthe influence of a third agent like sulfuric acid. Spinels of thetransition metals listed above may be utilized as effective, regenerablehydrogen sulfide sorbents; zinc aluminum spinel, as defined in U.S. Pat.No. 4,263,020, incorporated herein by reference, is a preferred spinelfor this invention. The sulfur capacity of spinels may be promotedthrough the addition of one or more additional metals such as Fe or Cuas outlined in U.S. Pat. No. 4,690,806, which is incorporated herein byreference.

Zeolitic materials may serve as hydrogen sulfide sorbents for thisinvention as detailed in U.S. Pat. No. 4,831,206 and -207, which isincorporated herein by reference. These materials share with spinels theability to function as regenerable hydrogen sulfide sorbents and permitoperation of this invention in a mode cycling between sulfur capture andsulfur release in either continuous or batch operation depending uponthe process configuration. Zeolitic materials incorporating sulfuractive metals by ion exchange are also of value to this invention.Examples include Zn4A, chabazite, and faujasite moderated by theincorporation of zinc phosphate, and transition metal frameworksubstituted zeolites similar to, but not limited to, U.S. Pat. No.5,185,135/6/7 and U.S. Pat. No. 5,283,047, and continuations thereof,all incorporated herein by reference.

Various derivatives of hydrotalcite (often referred to as LDH, layereddouble hydroxides) exhibit high sulfur capacities and for this reasonserve as hydrogen sulfide sorbents for this invention. Specific examplesinclude Mg₄.8 Al₁.2 (OH)₁₂ Cl₁.2, Zn₄ Cr₂ (OH)₁₂ Cl₂, Zn₄ Al₂ (OH)₁₂Cl₂, Mg₄.5 Al₁.5 (OH)₁₂ Cl₁.5, Zn₄ Fe₂ (OH)₁₂ Cl₂, and Mg₄ Al₂ (OH)₁₂Cl₃ and may include numerous modified and unmodified synthetic andmineral analogs of these as described in U.S. Pat. No. 3,539,306, U.S.Pat. No. 3,796,792, U.S. Pat. No. 3,879,523, and U.S. Pat. No.4,454,244, and reviewed by Cavani et al. in Catalysis Today, Vol. 11,No. 2, pp. 173-301 (1991), all of which are incorporated herein byreference. Particularly active hydrogen sulfide sorbents are LaRoachH-T, ZnSi₂ O₅ gel, Zn₄ Fe₂ (OH)₁₂ Cl₂, and the Fe containing clay,nontronite. A study of several Mg-Al hydrotalcites demonstrated apreference for crystallites less than about 300 Angstroms. Particularlynovel are pillared varieties of smectites, kandites, LDHs and silicicacids in which the layered structure is pillared by oxides of Fe, Cr,Ni, Co, and Zn, or such oxides in combination with alumina asdemonstrated by, but not limited to, U.S. Pat. No. 4,666,877, U.S. Pat.No. 5,326,734, U.S. Pat. Nos. 4,665,044/5 and Brindley et al, Clays AndClay Minerals, 26, 21 (1978) and Amer. Mineral, 64, 830 (1979), allincorporated herein by reference. The high molecular dispersions of thereactive metal make them very effective scavengers for sulfur bearingmolecules.

A preferred class of hydrogen sulfide sorbents are those which areregenerable as contrasted to those which bind sulfur irreversibly in astoichiometric reaction. Hydrogen sulfide sorbents which bind sulfurthrough physical adsorption are generally regenerable throughmanipulation of the process temperature, pressure, and/or gas rate sothat the sorbent may cycle between adsorption and desorption stages.Representative of such sorbents are zeolitic materials, spinels, meso-.and microporous transition metal oxides, particularly oxides of thefourth period of the Periodic Chart of the Elements.

Hydrogen sulfide sorbents which bind sulfur through a chemisorptivemechanism may also be regenerated by the use of reactive agents throughwhich the sulfur bearing compound is reacted and restored to itsinitial, active state. Reagents useful for the regeneration of thesetypes of hydrogen sulfide sorbents are air (oxygen), steam, hydrogen,and reducing agents such as carbon and carbon monoxide. The choice ofregenerating agent is determined by the initial, active state of thesorbent and by the chemical intermediates arising during theregeneration procedure. Active hydrogen sulfide sorbents regenerable byreaction with oxygen include the oxides of manganese, lanthanum,vanadium, tantalum, niobium, molybdenum, rhenium, zirconium, chromium,and mixtures thereof. Active hydrogen sulfide sorbents regenerablethrough reaction with steam, either alone or in combination with oxygen,include the oxides of lanthanum, iron, tin, zirconium, titanium,chromium, and mixtures thereof. Active hydrogen sulfide sorbentsregenerable through the sequential action of hydrogen and oxygen includethe oxides of iron, cobalt, nickel, copper, silver, tin, rhenium,molybdenum, and mixtures thereof. Active hydrogen sulfide sorbentsregenerable through the action of hydrogen include iron, cobalt, nickel,copper, silver, mercury, tin, and mixtures thereof. In addition alltransition metal oxides are regenerable from their correspondingsulfates by reduction with hydrogen, carbon, or carbon monoxide. Theseregeneration reactions may be facilitated by the inclusion of acatalytic agent that facilitates the oxidation or reduction reactionrequired to restore the sulfur sorbent to its initial, active condition.

In addition, of particular interest as regenerable hydrogen sulfidesorbents are two classes of materials: zeolitic materials enriched inthe alkali metals of Group IA; the high surface area, porous materialsrepresented by zeolite-like structures, nonstoichiometric basic oxidesof the transition metals, reviewed in part by Wadsley (NonstoichiometricCompounds, edited by Mandelkorn, Academic Press, 1964) and numeroussurfactant templated metal oxide materials analogous to MCM-41 typestructures as disclosed in U.S. Pat. No. 5,057,296 incorporated hereinby reference.

These regeneration processes operate over a temperature range of100-700° C., preferably 150-600° C., and more preferably 200-500° C. atpressures comparable to those cited below in the general disclosure ofprocess conditions common to this invention.

The hydrodesulfurization catalyst and the hydrogen sulfide sorbent usedin the practice of the present invention may be utilized in various bedconfigurations within the reactor. The choice of configuration may ormay not be critical depending upon the objectives of the overallprocess, particularly when the process of the present invention isintegrated with one or more subsequent processes, or when the objectiveof the overall process is to favor the selectivity of one aspect ofproduct quality relative to another. For example, bed configuration,catalyst formulation and/or process conditions can be varied to controlthe level of concomitant aromatics saturation. Mixed bed configurationstend to increase aromatics saturation relative to their stacked bedcounterparts. Also, higher metal loading, higher pressure and/or lowerspace velocity can lead to increased levels of aromatics saturation.

Various catalyst bed configurations may be used in the practice of thepresent invention with the understanding that the selection of aspecific configuration is tied to specific process objectives. Forexample, bed configuration, catalyst formulation and/or processconditions can be varied to control the level of concomitant aromaticssaturation. Mixed bed configurations tend to increase aromaticssaturation relative to their stacked bed counterparts. Also, highermetal loading, higher pressure and/or lower space velocity can lead toincreased levels of aromatics saturation. A bed configuration whereinthe hydrogen sulfide sorbent is placed upstream of the HDS catalyst isnot a configuration of the present invention.

Since the preferred HDS catalysts used in conjunction with the hydrogensulfide sorbent can simultaneously provide an ASAT function in thesystems described below, the HDS catalysts will hereafter be designatedas HDS/ASAT catalysts. However, the HDS catalyst is not required to havean ASAT function.

Various catalyst bed configurations may be used in the practice of thepresent invention. As disclosed above, the same catalysts identified forHDS in this process will preferably also be active for ASAT. Bedconfigurations based on three components are disclosed below. Onevariation utilizes a mixed HDS/ASAT catalyst and hydrogen sulfidesorbent bed upstream of a stand-alone ASAT catalyst; this genericarrangement is identified as the mixed/stacked configuration. The twobeds could occupy a common reactor or separate reactors. Separatereactors would be preferred if it is advantageous to operate thestand-alone ASAT catalyst at a substantially different temperature thanthe mixed bed of HDS/ASAT catalyst and hydrogen sulfide sorbentpreceding it. The HDS/ASAT catalyst in the mixed bed and the stand-aloneASAT catalyst may or may not be the same material.

A second variation is identified as the stacked/stacked/stackedconfiguration, where the three components are layered sequentially witha HDS/ASAT catalyst occupying the top position, the hydrogen sulfidesorbent the middle, and the stand-alone ASAT catalyst the bottom zone.While the three component systems may occupy a common reactor, thesesystems may utilize a multi reactor train. One multi reactorconfiguration would have the HDS/ASAT catalyst and a hydrogen sulfidesorbent occupying the lead reactor and the stand-alone ASAT catalystoccupying the tail reactor. Another multi-reactor configuration wouldhave and HDS/ASAT catalyst occupying the lead reactor and the hydrogensulfide sorbent followed by an ASAT catalyst in the tail reactor. Thesearrangement permits operating the two reactor sections at differentprocess conditions, especially temperature, and imparts flexibility incontrolling process selectivity and/or product quality. Alternatively,each component could occupy separate reactors. This would allow processconditions for each component as well as facilitate frequent orcontinuous replacement of the hydrogen sulfide sorbent material. TheHDS/ASAT catalyst and stand-alone ASAT catalyst may or may not be thesame material.

Noble metal catalysts can simultaneously provide HDS and ASAT functions.The ASAT activity of the catalyst can be maintained if said catalyst isintimately mixed with a hydrogen sulfide sorbent. The mixed bedconfiguration, as described above, allows operation in this mode. Ifthis configuration is employed, the use of a stand-alone ASAT catalystafter the mixed bed is optional, and said use would be dictated byspecific process conditions and product quality objectives. If employed,the stand-alone ASAT catalyst downstream may or may not be the samematerial as the HDS/ASAT catalyst used in the mixed bed. ASAT activitycan also be maintained in a stacked bed configuration, but activity willgenerally be at a lower level than the mixed bed configuration.

Materials can also be formulated which allow one or more of the variouscatalytic functions of the instant invention (i.e., HDS, ASAT) and thehydrogen sulfide sorbent function to reside on a common particle. In onesuch formulation, the HDS/ASAT and hydrogen sulfide sorbent componentsare blended together to form a composite particle. For example, a finelydivided, powdered Pt on alumina catalyst is uniformly blended with zincoxide powder and the mixture formed into a common catalyst particle, orzinc oxide powder is incorporated into the alumina mull mix prior toextrusion, and Pt is impregnated onto the zinc oxide-containing aluminain a manner similar to that described in U.S. Pat. No. 4,963,249, whichis incorporated herein by reference.

Another formulation is based on the impregnation of a support with aHDS/ASAT-active metal salt(s) (e.g., Pt, Pd, Ir, Rh) and a hydrogensulfide sorbent-active salt (e.g., Zn) to prepare a polymetalliccatalyst incorporating the HDS/ASAT metal(s) and the hydrogen sulfidesorbent on a common base. For example, a Pt-Zn bimetallic may beprepared in such a manner as to distribute both metals uniformlythroughout the extrudate, or, alternatively, the Zn component may bedeposited preferentially in the exterior region of the extrudate toproduce a rim, or eggshell, Zn rich zone, or the Pt component may bedeposited preferentially in the exterior region of the extrudate toproduce a rim, or eggshell, Pt rich zone. These are often referred to as"cherry" structures.

In any of the configurations described above, the catalyst componentsmay share similar or identical shapes and sizes, or the particles of onemay differ in shape and/or size from the others. The later relationshipis of potential value should it be desirable to affect a simple physicalseparation of the components upon discharge or reworking. Additionally,the hydrogen sulfide sorbent material can be sized to allow sorbentparticles to flow through a fixed bed of any combination of catalystsmoving with the liquid phase. In any of the stacked bed configurationswherein the hydrogen sulfide sorbent material is contained in a separatereactor, swing reactors can be employed such that one hydrogen sulfidesorbent reactor is always on-stream.

The composition of the sorbent bed is independent of configuration andmay be varied with respect to the specific process, or integratedprocess, to which this invention is applied. In those instances wherethe capacity of the hydrogen sulfide sorbent is limiting, thecomposition of the sorbent bed must be consistent with the expectedlifetime, or cycle, of the process. These parameters are in turnsensitive to the sulfur content of the feed being processed and to thedegree of desulfurization desired. For these reasons, the composition ofthe guard bed is flexible and variable, and the optimal bed compositionfor one application may not serve an alternative application equallywell. In general, the weight ratio of the hydrogen sulfide sorbent tothe HDS/ASAT catalyst may range from 0.01 to 1000, preferably from 0.5to 40, and more preferably from 0.7 to 30. For three componentconfigurations the ranges cited apply to the mixed zone of themixed/stacked arrangement and to the first two zones of thestacked/stacked/stacked design. The ASAT catalyst present in the finalzone of these two configurations is generally present at a weight equalto, or less than, the combined weight compositions of the upstreamzones.

The process of this invention is operable over a range of conditionsconsistent with the intended objectives in terms of product qualityimprovement and consistent with any downstream process with which thisinvention is combined in either a common or sequential reactor assembly.It is understood that hydrogen is an essential component of the processand may be supplied pure or admixed with other passive or inert gases asis frequently the case in a refining or chemical processing environment.It is preferred that the hydrogen stream be sulfur free, orsubstantially sulfur free, and it is understood that the lattercondition may be achieved if desired by conventional technologiescurrently utilized for this purpose. In general, the conditions oftemperature and pressure are significantly mild relative to conventionalhydroprocessing technology, especially with regard to the processing ofstreams containing the refractory sulfur types as herein previouslydefined. This invention is commonly operated at a temperature of 40-500°C. (104-932° F.) and preferably 225-400° C. (437-752° F.). Operatingpressure includes 100-3000 psig, preferably 100-2,200 psig, and morepreferably 100-1,000 psig at gas rates of 50-10,000 SCF/B (standardcubic feet per barrel), preferably 100-7,500 SCF/B, and more preferably500-5,000 SCF/B. The feed rate may be varied over the range 0.1-100 LHSV(liquid hourly space velocity), preferably 0.3-40 LHSV, and morepreferably 0.5-30 LHSV.

The process of this invention may be utilized as a stand alone processfor purposes of various fuels, lubes, and chemicals applications. Theinstant process may be combined and integrated with other processes in amanner so that the net process affords product and process advantagesand improvements relative to the individual processes not combined.Potential opportunities for the application of the process of thisinvention follow; these illustrations are not intended to be limiting.

Process applications relating to fuels processes include:desulfurization of FCC streams preceding recycle to 2nd stageprocessing; desulfurization of hydrocracking feeds; multiring aromaticconversion through selective ring opening (U.S. Ser. Nos. 523,299;523,300; 524,357; 524,358, filed Sep. 5, 1995 and incorporated herein byreference); aromatics saturation processes; sulfur removal from naturalgas and condensate streams. Process applications relating to themanufacture of lubricants include: product quality improvement throughmild finishing treatment; optimization of white oil processes bydecreasing catalyst investment and/or extending service factor;pretreatment of feed to hydroisomerization, hydrodewaxing, andhydrocracking. Process applications relating to chemicals processesinclude: substitute for environmentally unfriendly nickel basedhydroprocessing; preparation of high quality feedstocks for olefinmanufacture through various cracking processes and for the production ofoxygenates by oxyfinctionalization processes.

It has surprisingly been found by the inventors hereof that theinstantly claimed process is superior for meeting color specificationsof hydrocarbon products. Although color may have little impact on theactual quality and performance of a material, maintaining consistentcolor, over extended periods of time, is important to the refinerbecause the customer may expect a product of a certain appearance.

Conventional hydroprocessing and aromatics saturation technology areable to improve the color of a feedstock. However, conventionalhydroprocessing catalysts are often run at high temperature (³ 370° C.)to maximize HDS kinetics. This in turn requires higher and higherpressure to produce adequate catalyst lifetime and maintain overallproduct quality. The use of high temperature, even with high pressure,often produces a product with unsatisfactory color and/or colorstability. Examples 14 and 15 below illustrate the improved colorstability of the products produced in accordance with the presentinvention.

This invention is illustrated by, but not limited to, the followingexamples which are for illustrative purposes only.

EXAMPLES Preparation of Feedstock A (Partially Saturated CyclicFeedstock)

An aromatics solvent stream containing primarily C₁₁ and C₁₂naphthalenes with an API gravity of 10.0 was hydrogenated over 90 g (125cc) of a 0.5 wt. % Pd on alumina catalyst. The catalyst was prereducedin flowing hydrogen at 750° F. for 1 hour at atmospheric pressure. Thearomatics solvent feedstock was passed over the catalyst at 265° F., anLHSV of 1 with a hydrogen treat gas rate of 6000 SCF/B. Pressure wasinitially set at 400 psig and increased throughout the run to compensatefor catalyst deactivation to a final pressure of 700 psig. The productbalances were blended together to give a partially saturated productwith API gravity of 19.2.

Preparation of Feedstock B (Saturated Cyclic Feedstock)

An aromatics solvent stream containing primarily C₁₁ and C₁₂naphthalenes with an API gravity of 10.0 was hydrogenated over 180 g(250 cc) of a 0.6 wt. % Pt on alumina catalyst. The catalyst wasprereduced in flowing hydrogen at 750° F. for 16 hours at atmosphericpressure. The aromatics solvent feedstock was passed over the catalystat 1800 psig, 550° F., an LHSV of 1 with a hydrogen treat gas rate of7000 SCF/B. The saturated product had an API gravity of 31.6 and wasanalyzed to contain less than 0.1 wt. % aromatics and greater than 99wt. % naphthenes.

Preparation of Feedstock C

Feedstock C was prepared by blending 62 wt. % of Feedstock B with 38 wt.% of Feedstock A and spiking to 44 wppm S with4,6-diethyldibenzothiophene. The feedstock had an API gravity of 23.7and contained 55 wt. % aromatics as measured by SFC.

Preparation of Feedstock D

Feedstock D was prepared by blending 62 wt. % of Feedstock B with 38 wt.% of Feedstock A and spiking to 47 wppm S with4,6-diethyldibenzothiophene. The feedstock had an API gravity of 23.7and contained 53 wt. % aromatics as measured by SFC.

Example 1

A reactor was charged with a mixed bed of 1.27 g of a 0.6 wt. % Pt ongamma alumina catalyst and 2.94 g of a ZnO. This catalyst was used toprocess Feedstock C. The product gravities and aromatics content weremeasured to follow catalyst activity and stability for the integratedHDS and aromatics saturation reactions with time on oil. Successfulconversion of aromatics to naphthenes is accompanied by an increase ingravity. The results are presented in Table 1 where a high level ofactivity was sustained for about 575 hr. on oil.

                  TABLE 1    ______________________________________    Processing of Feedstock C at 300° C., 650 psig,    5000 SCF/B H.sub.2, and 1 LHSV (over Pt)    Example Catalyst Hr. On Oil                              API Gravity                                       Wt. % Aromatics    ______________________________________    1       Pt + ZnO 95       31.7     0.6    1       Pt + AnO 573.75   31.6     0.7    2       Pt/ZnO   95       29.8     11.0    2       Pt/ZnO   432.5    28.5     17.6    2       Pt/ZnO   526.75   28.5     19.5    ______________________________________

Example 2

The procedure of Example 1 was followed except that the zinc oxide wasplaced after the 0.6 wt. % Pt catalyst in a stacked bed configurationinstead of in a mixed bed configuration. The catalyst was used toprocess Feedstock C. The product gravities and aromatics levels listedin Table 1 illustrate reduced initial saturation activity compared tothat of Example 1. In addition, catalyst activity decreases between 95and 432.5 hours on oil and then stabilizes at a low level of activity.

Example 3

The catalyst system of Example 1 was used to process Feedstock C at of6.0 over Pt. The product gravity and aromatics level listed in Table 2illustrates comparable activity to the catalyst system of Example 2 at aspace velocity which is 6 times higher.

                  TABLE 2    ______________________________________    Processing of Feedstock C at 300° C., 650 psig and 5000 SCF/B    H.sub.2                      LHSV               Wt. %    Example Catalyst  (over Pt) API Gravity                                         Aromatics    ______________________________________    2       Pt/ZnO    1.0       28.5     19.5    3       Pt + ZnO  6.0       29.0     13.7    ______________________________________

Example 4

The catalyst system of Example 1 was used to process Feedstock C at anLHSV of 8.0 over Pt. The product gravity and aromatics level is listedin Table 3.

Example 5

The catalyst system of Example 2 was used to process Feedstock C at anLHSV of 2.0 over Pt. The product gravity and aromatics level in Table 3illustrates similar activity to the catalyst system of Example 4 at aspace velocity which is 4 times lower. Tables 2 and 3 clearly show thesuperior activity of the mixed bed system for aromatics saturation ascompared to the stacked bed.

                  TABLE 3    ______________________________________    Processing of Feedstock C at 300° C., 650 psig and 5000 SCF/B    H.sub.2                      LHSV               Wt. %    Example Catalyst  (over Pt) API Gravity                                         Aromatics    ______________________________________    4       Pt + ZnO  8.0       27.2     24.8    5       Pt/ZnO    2.0       27.3     24.9    ______________________________________

Example 6

A reactor was charged with a mixed bed of 0.62 g of a 0.3 wt. % Pt ongamma alumina catalyst and 7.5 g of a ZnO. This catalyst system was usedto process Feedstock D. The product gravity, aromatics content, andsulfur level were measured to follow catalyst activity at various spacevelocities for the integrated HDS and aromatics saturation reactions.The results are presented in Table 4.

                  TABLE 4    ______________________________________    Processing of Feedstock D at 300° C., 650 psig, and 5000 SCF/B    H.sub.2                     LHSV      API    Wt. %  Sulfur,    Example Catalyst (over Pt) Gravity                                      Aromatics                                             wppm    ______________________________________    6       Pt + ZnO 2         26.5   33.7   >1    6       Pt + ZnO 10        24.3   50.5   18    7       Pt/ZnO   1         25     45.3   10    7       Pt/ZnO   3.5       24.1   51.0   18    7       Pt/ZnO   10        24.0   53.0   33    ______________________________________

Example 7

A reactor was charged with a stacked bed of 0.62 g of a 0.3 wt. % Pt ongamma alumina catalyst followed by 5.72 g of a ZnO. The catalyst wasused to process Feedstock D. The product gravity, aromatics content, andsulfur level were measured to follow catalyst activity at various spacevelocities for the integrated HDS and aromatics saturation reactions.The results are presented in Table 4 and illustrate lower activity ofthe stacked bed system for HDS and aromatics saturation as compared tothe mixed bed catalyst system of Example 6. When the catalyst systems ofExample 6 and 7 are compared at 10 LHSV, the product sulfur level fromthe mixed bed is almost two times lower than that from the stacked bed.To reach a product sulfur level of 18 wppm, the LHSV over the stackedbed is approximately three times lower than that required by the mixedbed. The mixed bed produces a product with <1 wppm S at an LHSV of 2while the stacked bed produces a product with 10 wppm S at an LHSV of 1.

Example 8

A reactor was charged with a mixed bed of 2.9 g of a 0.6 wt. % Pt ongamma alumina catalyst and 1.7 g of zinc oxide. The mixed catalystsystem was used to process a hydrotreated light cat cycle oil with APIgravity of 26 containing 5 wppm sulfur, <1 wppm nitrogen and 55 wt. %aromatics. Successful conversion of aromatics to naphthenes isaccompanied by an increase in gravity, and the stability of the catalystis reflected in changes in gravity with time on oil. Product gravity wasmeasured to follow catalyst stability for the aromatics saturationreaction with time on oil. The results are presented in Table 5 where ahigh level of activity was sustained for about 140 hr on oil.

Example 9

A reactor was charged with a mixed bed of 2.9 g of a 0.6 wt. % Pt ongamma alumina catalyst and 1.7 g of zinc oxide. This bed was placedupstream of a 0.9 wt. % Ir catalyst. This catalyst system was used toprocess the feed of Example 8. The product gravity and aromatics contentwere measured to follow catalyst stability for the integrated aromaticssaturation and ring opening reactions with time on oil. Successfulconversion of aromatics to naphthenes, and naphthenes to paraffins, isaccompanied by an increase in gravity over that observed in Example 8.The results are presented in Table 5 where a high level of activity wassustained for about 140 hr on oil.

Example 10

The procedure of Example 9 was followed except that no zinc oxide wasadmixed with the Pt catalyst. This configuration provides no hydrogensulfide sorbent. The catalyst system was used to process the feed ofExample 8. The product gravities and aromatics level listed in Table 5illustrate retention of aromatics saturation activity but significantlyreduced ring opening activity compared to that of Example 9 on the 5wppm sulfur feed. Note: sulfur poisoning of hydrogenolysis activity(i.e., selective ring opening) is known to occur at substantially lowersulfur levels than required to poison aromatics saturation activity.

                  TABLE 5    ______________________________________    Processing of LCCO Containing 5 wppm S, <1 wppm N and    55 Wt. % Aromatics 315°°C., 650 psig, 5000 SCF/B H.sub.2,    0.75 LHSV (over Pt)                 API Gravity                           Wt. % Aromatics                 @ Hr on Oil                           @ Hr On Oil    Example  Catalyst  45       136  136    ______________________________________    8        Pt + ZnO  32.8     32.9 3.3    9        Pt + ZnO/Ir                       33.8     33.7 1.9    10       Pt/Ir     33.3     33.2 2.0    ______________________________________

Example 11

The catalyst system of Example 8 was used to process a secondhydrotreated light cat cycle oil with API gravity of 27 containing 60wppm sulfur, 1 wppm nitrogen and 56 wt. % aromatics. Product gravity wasmeasured to follow catalyst stability for the aromatics saturationreaction with time on oil. Table 6 shows no loss in catalyst performancewhen operated on the second, higher sulfur feed.

Example 12

The catalyst system of Example 9 was used to process the feed of Example11. Product gravity was measured to follow catalyst stability for theintegrated aromatics saturation and ring opening reactions with time onoil. Table 6 shows no loss in catalyst performance when operated on thesecond, higher sulfur feed.

Example 13

The catalyst system of Example 10 was used to process the feed ofExample 11. Product gravity was measured to follow catalyst stabilityfor the integrated aromatics saturation and ring opening reactions withtime on oil. Table 6 shows inferior performance of this catalyst systemon the 60 wppm sulfur feed. This is due to the inability of the systemto protect the ring opening activity of the highly sulfur-sensitive Ircatalyst, as well as reduced aromatics saturation activity of the Pt andIr catalysts.

                  TABLE 6    ______________________________________    Processing Of LCCO Containing 60 wppm S, 1 wppm N and 56 Wt. %    Aromatics    315° C., 650 psig, 5000 SCF/B H.sub.2, 0.75 LHSV (over Pt)                 API Gravity                           Wt. % Aromatics                 @ Hr on Oil                           @ Hr On Oil    Example  Catalyst  48       92   92    ______________________________________    11       Pt + ZnO  32.8     32.8 3.4    12       Pt + ZnO/Ir                       34.0     33.8 1.8    13       Pt/Ir     32.6     32.2 8.1    ______________________________________

Example 14

A reactor was charged with mixed bed of 2.9 g of a 0.6 wt. % Pt/aluminacatalyst and 1.7 g of a zinc oxide. This catalyst system was used toprocess a hydrotreated light cat cycle oil with API gravity of 27.1containing 60 wppm sulfur, 1 wppm nitrogen and 56 wt. % aromatics. Theproduct gravity, aromatics content and sulfur level were measured. Theresults presented in Table 7 indicate that HDS and aromatics saturationreactions are occurring simultaneously.

Example 15

A reactor was charged with mixed bed of 0.6 g of a 0.3 wt. % Pt/aluminacatalyst and 7.7 g of a zinc oxide. This catalyst system was used toprocess the feed of Example 14. The product gravity, aromatics contentand sulfur level were measured at various space velocities. The resultspresented in Table 7 indicate that HDS can be largely decoupled fromaromatics saturation by choice of catalyst, bed configuration andprocess conditions.

                                      TABLE 7    __________________________________________________________________________    Processing of LCCO Containing 60 wppm S, 1 wppm N and 56 wt. % Aromatics    650 psig and 5000 SCF/B H.sub.2                       LHSV API  Wt. %                                      Sulfur,    Example          Catalyst                Temp., ° C.                       (over Pt)                            Gravity                                 Aromatics                                      wppm    __________________________________________________________________________    14    0.6 Pt + ZnO                315    0.75 32.8 3.4  <1    15    0.3 Pt + ZnO                300    9.9  27.4 47.7 <1    15    03. Pt + ZnO                300    22.3 27.3 48.7 <1    __________________________________________________________________________

Example 16

A severely hydrotreated LCCO with a ASTM color of +2.5 was processedover a 0.6 wt. % Pt on gamma alumina catalyst at 288° C., 1800 psig, and5000 SCF/B H₂. The feed contained 5 wppm S and 55 wt. % total aromatics.

One run was performed without zinc oxide admixed with the platinumcatalyst at a liquid hourly space velocity of 1.0. A second run wasperformed with zinc oxide (4:1 0.6% Pt on Al₂ O₃ /ZnO) at a liquidhourly space velocity of 1.7. Both products initially had Saybolt colorsof³ +20. Samples of the two products left in glass bottles (exposed tolight) showed different color stabilities. The sample processed withoutzinc oxide had a final Saybolt color of -10, while the sample processedwith zinc oxide retained a Saybolt color of³ +20.

Example 17

A basestock sample was prepared from "finished" 250 SN (solvent neutral)lube basestock which was then subjected to raffinate hydroconversionconditions (1200 psig) and topped for removal of light ends. This feedwas then subjected to further hydroprocessing.

In one, the feed basestock was treated at 250° C., 1000 psig, 3000 SCF/BH₂, 1.0 LHSV over a stacked bed of 1) 0.6% Pt on Al₂ O₃ /ZnO and 2) 0.9%Ir/Al₂ O₃. Under these conditions only hydrogenation and no ring openingwould be expected (too low in temperature). The product was clear andhad a Saybolt color of³ +20, with essentially no boiling rangeconversion to fuels.

In another run, the feed basestock was treated at 260° C.), 1000 psig,3000 SCF/B H₂, 1.0 LHSV over a stacked bed of 1) 0.6% Pt on Al₂ O₃ /ZnOand 2) a commercial aromatics saturation catalyst available from Zeolystas Z-714A. The product was clear and had a Saybolt color of³ +20, withabout 10% boiling range conversion to fuels and light ends.

After topping to remove fuels/light ends, these two hydroprocessedbasestock samples, plus a reference sample of the feed, were placed insmall, capped vials and exposed to ambient sunlight from a south-facingwindow (window did have UV shield screen). After 35-40 days, the feedbasestock sample (initial Saybolt color of -5) had a ASTM color of 3.5with some brown sediment and a bit of haze. The product of the first runhad a Saybolt color of -5 and was just beginning to show some haze. Theproduct of the second run had a Saybolt color of ³ +20 and wascompletely clear (no haze).

Examples 16 and 17 demonstrate that with the process of the presentinvention it is possible to improve both the initial color and colorstability of distillate and lube products.

What is claimed is:
 1. A process for the substantially completedesulfurization of condensed ring sulfur heterocyclic compounds and thesaturation of aromatic compounds of distillate petroleum streamscontaining said compounds, which process comprises contacting said,stream at temperatures from about 40° C. to 500° C. and pressures fromabout 100 to 3,000 psig, with a catalyst system comprised of: (a) acatalyst comprised of a noble metal selected from the group consistingof Pt, Pd, Ir, Rh, and polymetallics thereof, on an inorganic refactorysupport; and (b) a hydrogen sulfide sorbent material; wherein both thecatalyst and the hydrogen sulfide sorbent material are present on thesame composite particles.
 2. The process of claim 1 wherein the level ofsulfur in the feedstream is less than about 1,000 wppm.
 3. The processof claim 1 wherein the noble metal is selected from Pt, Pd, Ir, andpolymetallics thereof.
 4. The process of claim 2 wherein the hydrogensulfide sorbent material is selected from supported and unsupportedmetal oxides, spinels, zeolitic based materials, and hydrotalcites. 5.The process of claim 2 wherein the hydrodesulfurization catalyst ispromoted with one or more metals selected from the group consisting ofRe, Cu, Ag, Au, Sn, Mn, and Zn.
 6. The process of claim 1 wherein theconcentration of noble metal is from about 0.01 to 3 wt. %, based on thetotal weight of the catalyst.
 7. The process of claim 2 wherein theinorganic refractory support is selected from the group consisting ofoxides of Al, Si, Mg, B, Ti, Zr, P, and mixtures and cogels thereof. 8.The process of claim 2 wherein the inorganic refractory support isselected from clays and zeolitic materials and mixtures thereof.
 9. Theprocess of claim 8 where the zeolite is enriched with one or more metalsof Group Ia of the Periodic Table of the Elements.
 10. The process ofclaim 2 wherein the hydrogen sulfide sorbent is a metal oxide of metalsfrom Groups IA, IIA, IB, IIB, IIIA, IVA, VB, VIB, VIIB, and VIII of thePeriodic Table of the Elements.
 11. The process of claim 10 wherein themetal is selected from the group consisting of K, Ba, Ca, Zn, Co, Ni,and Cu.
 12. The process of claim 1 wherein the hydrodesulfurizationmetal and the metal of the hydrogen sulfide sorbent are precipitated onthe same support material.
 13. The process of claim 1 wherein thepressure is from about 100 to 1,000 psig.
 14. The process of claim 3wherein the pressure is from about 100 to 1,000 psig.